Japanese Patent Laid-Open Nos. Hei 2-168021 and Hei 6-52536 show rolling bearings whose oil film forming capability has been improved by micro-concavoconvexes on the surfaces of rolling elements. In this prior art, measures are taken against damage, such as peeling damage, to the roller bearing due to poor lubrication, by providing microconcave-like pits in the rolling surfaces of the rollers or the rolling contact surfaces of the rollers and/or the raceway surfaces of the inner and outer rings, so that with the surface roughness denoted by the parameter Rqni, the ratio Rqni (L)/Rqni (C)≦1.0, where Rqni (L) is the axial surface roughness and Rqni (C) is the circumferential surface roughness, and the surface roughness parameter Sk value≦−1.6, thereby ensuring a long life irrespective of whether the mating surface is a rough or well-finished surface.
In automobile transmissions and other regions where rolling bearings are used, the trend toward size reduction and high output attainment has been advancing more and more in recent years, and the usage environment, including the use of low viscosity lubricating oils, tends to higher loads and higher temperatures. For this reason, the lubrication environment is changing to one that is more severe than ever before for bearings, so that wear due to poor lubrication, surface-start abrasion, decreased fatigue life, and abrasion under conditions of foreign-matter inclusion are tending to occur more easily. Accordingly, it is necessary to ensure that life extension can be attained under any lubricating conditions, including low viscosity harsh lubrication, foreign-matter inclusion environment, and clean lubrication.
Conventional microconcave-like pits are such that with the surface roughness denoted by the parameter Rqni, the ratio Rqni (L)/Rqni (C) is 1.0 or below (Rqni≧0.10), where Rqni (L) is the axial surface roughness and Rqni (C) is the circumferential surface roughness, and the surface roughness parameter Sk value is −1.6 or below, thereby ensuring a long life irrespective of whether the mating surface is a rough or well-finished surface. In the case where the oil film is extremely thin under lean lubrication, however, there are cases where its effects cannot be fully developed.